The Children's Cancer Study Group A is composed of a group of cooperative pediatric centers, and provides an administrative and communicative structure for the performance of cooperatively designed clinical studies for the treatment of children with leukemia and solid tumors. These investigations involve a multidisciplinary approach including multiple-agent chemotherapy, surgery, radiation, immunotherapy, and other modalities. The objective of these studies is to establish with maximum efficiency therapeutic regimens for these diseases that will provide an optimal outcome, with minimal untoward effects.